Gestalt rules clarification

I am playing in a D&D 3.5 game. We are level 5 gestalt with 2 free LA (as in if you have a race or template with LA, you can get up to 2 total of them for free. Any Racial HD are paid as normal).

I chose a water orc (0 LA) with the natural lycanthrope template, Weretiger version (3LA normally, 1 with the rules. and with 3RHD). On one side of my Gestalt, I put 4 levels of Warblade and 1 level of Warshaper. On the other I put the LA of the weretiger, and 4 levels of the Weretiger class.

We had down how our characters were going to progress and for the next 2 levels, I put 2 more levels of Warshaper and 2 more levels of weretiger and the other side had 2 more levels of Weretiger.

This is where I need help because at this point, I started to progress Warblade and Warshaper at the same time, which I was told I could not do, as you can not move the side a gestalt class is on. I cannot find any such restriction on the d20SRD page, and I can also not find the source book for gestalt rules. I looked in PHB1&2 as well as the DMG1&2.

Is this a rule in the gestalt ruleset, or is it a houserule? Also, what specific book or books were gestalt rules introduced in?

If my explanation didn’t make sense, I put down a visual aid below this:

lvl 1: WeretigerLA |||| Warblade 1

lvl 2: Weretiger 1 |||| Warblade 2

lvl 3: Weretiger 2 |||| Warblade 3

lvl 4: Weretiger 3 |||| Warblade 4

lvl 5: Weretiger 4 |||| Warshaper 1

lvl 6: Weretiger 5 |||| Warshaper 2

lvl 7: Weretiger 6 |||| Warshaper 3

lvl 8: Warshaper 4 |||| Warblade 6

lvl 9: Warshaper 5 |||| Warblade 7