It doesn’t. It’s a well accepted grammar error that would be marked wrong by perhaps 100% of native speakers who saw it, which is the gold standard for deciding what is “right” or “wrong” in terms of grammar.
And most native speakers don’t know the difference between syntax and semantics, but there’s no reason to be sloppy when you’re talking in a context where the difference might be important or useful. The rules of syntax may be determined by corpus linguistics, but that doesn’t mean that every time someone says “this is wrong” it means “this violates the rules of English grammar.”
IOW, if somebody says “write a picture” is bad grammar, they’re wrong, or they don’t know what grammar is. There is absolutely no difficulty in parsing “write a picture” as English.
The only thing you can make the welkin do is ring.
“Write a picture” is a well-known grammar error, if only you did the research I suggested.
It is also very early in the morning for me yet I have an MA in a related field and have been teaching grammar for ~20 years.
Many things are “well known” grammar errors that have nothing at all to do with grammar. A simple parse of the phrase in question is enough to correspond its structure with one of the most basic units of English syntax:
[[sub]VP[/sub] write a picture] = [[sub]VP[/sub] [[sub]V[/sub] write] [[sub]NP[/sub] a picture]] => [[sub]VP[/sub] [[sub]V[/sub] write] [[sub]NP[/sub] [[sub]D[/sub] a] [[sub]N[/sub] picture]]]
To claim that merely nonsense phrases are bad grammar is to blur the definition of grammar to the point of uselessness. It would be like saying that dropping an anvil on your foot is bad metallurgy: sure, there’s a connection there, but no, not really.
Seriously, you’re trying to drop that UG crap to win an argument? Green dreams sleep furiously?
Again, see what I posted.
“Green dreams sleep furiously” is nonsense but good grammar. Really, why are you so insistent on making syntax do a job that it’s not meant to do? If you could point out to me where in a reputable book on grammar by actual linguists (CGEL for example) it lists the rule by which “write a picture” can be judged ungrammatical, I would happily concede the point.
EDIT: and you leave my grampapa alone! :o
Go ahead and pick up any writing or grammar text written in the past 10 years. There’s probably numerous sections on why word choice/collocation errors are real, accepted errors.
Errors, yes. Syntax errors, no.
EDIT: it strikes me that perhaps the root of this disagreement is that I’ve been using “grammar” to mean precisely “syntax,” but you might mean it more broadly. I’d hoped this was implied when I drew the distinction between “language” and “grammar” wrt njtt’s post, but if that’s all this is about then I retract my belligerent corrections. 
No problem.
Well, in my defense I’ll only say that in linguistics, “grammar” usually does refer only to morphology and syntax. In my field (computer science, admittedly a bit removed from human linguistics), it does so exclusively.
Apropos “write a picture”, following the katharevousa Greek idiom the proper verb for what an Eastern Orthodox iconographer does in creating one, which most of us would use “draw and paint” as the relevant verbs, is “to write an icon.” The reference, as I understand it, is to the symbology appropriate to each saint’s iconology.
Though a quite specialized usage, I’d have to say it is grammatically sound English.
Sigh.
I’m with Polycarp on this one. He said it was grammatically spund, and I completely agree.
I figured you would.
Notwithstanding that Polycarp’s argument relates to Greek, I still challenge you to find any evidence of unspundness. I am quite sure none exists.
EDIT: of course now I see that Polycarp has corrected his post and thereby rendered me ridiculous.
Unspundification has a long history.
Not true – Legs can also be akimbo. I thought of naming a character “‘Legs’ Akimbo”, but shortly afterwards, the comic strip Meek and Eek did just that.