Someone suggested that Tamiya may have changed their formula and can no longer be thinner with lacquer thinner. I got a gloppy oily mess this time.
from this discussion
http://cs.finescale.com/fsm/feedback_help_and_testing/f/22/p/151747/1626300.aspx#1626300
may be the answer you need.
HTH 
Which brand lacquer thinner did you use? Not all lacquer thinners are the same, so it does matter.
I still thin Tamiya paint with Tamiya’s own lacquer thinner without problems (for airbrushing, at least).
I used Klean Strip. The old can was bought a while back. new can is exactly the same. Given the result I am guessing they have changed something in their formula and it’s not the paint. Used alcohol on the last build without issue.
I just used some recently-purchased Tamiya XF-1 with Mr. Leveling Thinner last night without problem.