This is the character in question
https://www.dndbeyond.com/profile/Madrummer/characters/32200619
The spell slots for a 17 Arcane Rogue / 3 Sorcerer should not be what this sheet is showing, right?  I shouldn't have any 4th level spell slots, and less on the others, right?  But if you go to the spells tab and check the spell slots, it shows 4/3/3/2 for lv1-4 spell slots.

So am I missing something here, or is the system just making a mistake on calculating spell slots?

In case that link doesn't work for you
http://ddb.ac/characters/32200619/SvMTyV

 From the Spellcasting portion of the rules that mention Multi-Class.

Spell Slots. You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, and half your levels (rounded down) in the paladin and ranger classes. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.

If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slots, but only to cast your lower-level spells. If a lower-level spell that you cast, like burning hands, has an enhanced effect when cast using a higher-level slot, you can use the enhanced effect, even though you don't have any spells of that higher level.

For example, if you are the aforementioned ranger 4/wizard 3, you count as a 5th-level character when determining your spell slots: you have four 1st-level slots, three 2nd-level slots, and two 3rd-level slots. However, you don't know any 3rd-level spells, nor do you know any 2nd-level ranger spells. You can use the spell slots of those levels to cast the spells you do know — and potentially enhance their effects.

So you can upcast spells cause you count as a 20th level spell caster, but you cant learn spells of that level. Hopefully that helps (not an expert in this by any means).

Edit: Bolded by me for emphasis

You are a multiclassed spell caster, that means your spell slots available follow the multi class spellcasting rules.  I'd look over that in the PHB.  But to just tell you since you have 3 levels of sorcerer you add those three plus 1/3 of your Arcane trickster rounded down.  So you get 3 + 5 = 8.  So you are an 8th level caster which gets 4/3/3/2 slots. 

Oh damn!  Thank you so much, I didn't even think of the multiclass spell casting rules being applied.  It's been so long since I've played a multiclass character and one that's a spellcaster that it totally went right over my head.

Thank you guys for the reply.