cell line adherence - cells adhering to flask very tightly after transfectiono (Feb/01/2011 )

Hi,
I am transfecting 293T/17 cells with mutants in an episomal vector using Lipofectamine 2000 and then trypsinising them to collect the cells. With some of the mutants the cells are adhering so strongly to the bottom of the flask that no matter how long I incubate them with trypsin, they wont come off the flask. This is consistently only some of the mutants and not others despite all cells being treated in exactly the same manner. Ca anybodyd suggest why this could be? Is it likely that this is the effect of my protein or is it something else? If it is a functional effect of expressing these mutants in the cells, is there an assay that I can do to measure this and compare the mutants?
Thanks,
Elle

You are transfecting them with mutant what?

I'm not sure what the reason for the variability is, but is scraping them a viable alternative to trypsinising?