actually not all that surprised by this. The Lib Dems support in Labour areas like Glasgow and Cardiff will have partly come from disaffected/protest voting ex-Labour people, turned away by the war and tuition fees and stuff. It should really be no surprise that a handful of those voters would switch to voting TUSC - although with these two places there's also the fact there's viable left-ish nationalist parties, no doubt they've taken a big share of the ex-Lib Dem voters too. Amongst those ex-LD voters who won't vote Labour there's a range of possibilities (UKIP, TUSC, Green, SNP/Plaid...) for them to vote for instead of the LIb Dem.
The share of the vote is too low to really read deeply into anyway, looking at these results on this thread i'd say the Lib Dems are in deep trouble, Labour are winning everywhere they ought to, UKIP's vote isn't just the polls it's real and the "others" section of fringe parties will keep getting higher and higher.