Astral construct doesn’t have that limit
The Complete Psionic update of this power is invalid under the rules and should be ignored.
When you find a disagreement between two D&D® rules sources, unless an official errata file says otherwise, the primary source is correct.
(Any D&D 3.5e errata file)
The primary source of astral construct is Expanded Psionics Handbook. If Wizards of the Coast wanted to change how astral construct works, under their own rules they needed to issue an erratum for Expanded Psionics Handbook to that effect. According to their own rules, Complete Psionic cannot change Expanded Psionics Handbook’s material. See our Q&A about a similar situation regarding Rules Compendium for more details.
Astral construct shouldn’t have that limit
The Complete Psionic update of this power is undesirable for the game and should be ignored.
Expanded Psionics Handbook is one of the best-written books for D&D 3.5e. Complete Psionic is one of the worst. Astral construct is a cool, flavorful power that is, in a lot of ways, emblematic of what psionics “means” in D&D 3.5e. Complete Psionic, on the other hand, is routinely rumored to have been authored by at least one person who hated psionics. Which is why we have complete and utter travesties of the flavor and lore, in the form of divine mind, Illithid Heritage, and similar. It’s also why we have absolutely unnecessary nerfs to things that were fine, most notably astral construct. The Complete Psionic version of astral construct is close to garbage.
Please do not ruin psionics in your game by letting Complete Psionic tell you what psionics is. There are a few decent things in there (most notably the ardent), but it is a bad, bad book, and it blatantly does not know what psionics is. I am telling you this as a fan, but also as someone who has been published for writing psionics content (for Pathfinder 1e, a D&D 3.5e spin-off).
Schism doesn’t let you get around limits like that
A limit that was written as “your mind can only hold onto one of these at a time,” schism would help, because it gives you two minds. There is maybe an argument that any limitation on a psionic power like this is a mental one, because it’s psionics, but that doesn’t really hold up because psionics is often more whole-body than that—and you still only have one body, one interface to the external world.
But most notably, in this case, is the fact that Complete Psionic wrote “The exception is if you are a 5th-level ectopic adept,” when they were aware of schism and could have written it in there if they intended it be an option. As I said above, I think you absolutely should ignore their intent, but both what they wrote and what they clearly intended does not allow schism to help.