Yeah, SPAT is quite buggy.
Sometimes the one spell per turn limit only applies to the player while the AI can cast as many spells as it sees fit. On other occasions, it's vice versa.
I haven't experienced the bug you've described regarding the unability to cast spells, though. You might want to try downloading the attached .dck file and check if the problem is persistent when using that deck. I'd assign a deck that doesn't include any special rules card to the AI for testing purposes.
The game often crashes on either player's turn - sometimes with error dumps, sometimes without. Even if you construct a deck full of vanilla creatures, it.will.crash.
The infinite mana rule is problematic, too: the AI will abuse the living hell out of activated abilities that don't require tapping.
As for Planechase, make sure that both you and thw AI use a deck consisting of the actual deck and a Planechase rules card. If only one player has that rules card in the deck, neither player will be able to roll the Planar Die. You don't need to put specific Planes into the decks, as both players will use a shared Planes deck which includes all Planes available in Manalink. There might be a way to choose the Planes that are used, but I'm not familiar enough with the mode to tell you how.
Once you are in a game with two decks that have the Planechase rules card (+ actual cards to play with), you simply need to click the gold-bordered Planechase rules card to roll the die. The first roll of your turn costs

, the second costs

, the third

and so on and so forth. The amount of mana that has to be paid for the next roll is represented by counters that are automatically put on the Planechase rules card.
You will planeswalk from one plane to another when the planeswalker symbol comes up on the die. There is no animation for the roll in Manalink, but a popup window will provide information on its outcome.
Planechase mode seems to work fine; i haven't experienced any crashes, bugs or showstoppers during the handful of games I've played.
Sidenote: Seeing as these are bonus modes and considering that at any given time of Manalink's development the number of developers working on the code has been minimal, it really shouldn't be too surprising that stuff like SPAT has been overlooked. After all, there is still a long backlog of individual card bugs and missing functionality (
Stifle and
Misdirection being uncodeable, approximations, triggers not using stack, unability to process stack step by step, cards coded in ASM etc.) and I'm glad that the devs focus on these things rather than on alternative game modes.
EDH/Commander functionality has improved a lot thanks to Gargaroz and Korath, though
