Believe it or no, problem is not solved until these days... Anyway, I gave up trying to figure out what is wrong and my conclusion is pretty much same as yours.
I have 4 textarea extrafields that can be large (large like they need longtext field type in database, I had to change that too). As soon as entries become 3-4 A4 pages of text approx - editing is stuck beyond time expiration for script execution. It goes up to 3 minutes, which noone normal will wait today!
File administrator/components/com_k2/lib/JSON.php, line around 497,
function decode($str) {
....
}
Change whole that function in just
function decode($str)
{
return json_decode($str);
}
This is if you use php 5.2+ and I suppose there's noone who doesn't today.
What I don't know is if this leaves some other consequences in therms something can not be decoded, since encode function is also K2 custom made. Maybe it can be replaced too, but for now I am not touching it. Everything started working lightning fast, like in 1 second or so...
I hope this helped, cheers!
